Add global enable for recursion call

Hi fabinp, thank you for powerful module, and I'm make some change for recursion call  profiling.

here is case:

    def test_inner_func():
        c = dict((i, i*2) for i in xrange(10000))
        
        def inner_func():
            inner_c = [1] * 1024 * 1024 * 5
            return inner_c
        
        inner_func()

In the `test_inner_func`, I need know profile of every sub call normally. so, i'm add an argument for enable the global switch to do this.

demo:

    from memory_profiler import LineProfiler as MemeryProfiler, show_results
    mp = MemeryProfiler(enable_global=True)
    @mp
    def test_inner_func():
        c = dict((i, i*2) for i in xrange(10000))
        
        def inner_func():
            inner_c = [1] * 1024 * 1024 * 5
            return inner_c
        
        del c
        inner_func()

        import os
        dirs = list(os.walk("."))